Brain injury and neurodegenerative disorders cause significant losses of brain cells. Classical treatment strategies are limited, and the need to find therapies promoting the formation of BOTH neurons and blood vessels is gaining wide recognition. Sphingosine-1-phosphate is a lipid mediator exerting plettropic effects of a wide variety of cell types, including glial cells, neurons and endothelial cells (EC). These cell type not only proliferate in response to S1P, but also express the S1P synthesizing enzyme SPK2. We therefore propose 3 specific aims to test in vitro and in vivo the hypothesis that S1P derived from neurons and EC acts as an autocrine and paracrine trophic factor, activating S1P1 receptors on various brain cells types, thereby initiating ERK signaling (neural progenitors) or the Akt/endothelial nitric oxide synthase cascade (EC), and promoting CONCERTED angiogenesis and neurogenesis. Aim 1 will confirm and characterize the proliferation-inducing effect of S1P on EC and neural progenitor cells (NPC). We propose that these effects are not only mediated directly via S^P^ receptors, but also via the synthesis and release of "classical" growth hormones such as VEGF. Limited gene array analysis of factors released by SIP-stimulated cells will be performed to test this hypothesis. Aim 2 will extend preliminary findings showing that neurons and EC are a relevant source of S1P during stroke and that neuron- and EC-derived S1P mediates the proliferation of brain EC and NPC observed in Aim 1. With the use of specific inhibitors, receptor agonists, RNA interference technology and transgenic mice, we will determine the role of the SPK2 subtype, and whether S1P mediates its proliferative effects via S1P1 receptors. Aim 3 will examine the in vivo significance of SPK2 up-regulation and the activation of the SIP^Akt/eNOS system following ischemia in mice. We hypothesize that administration of a specific S1Pi receptor agonist or FTY720 (a pro-drug converted to a S1P receptor agonist by SPK2, but not SPK1) will enhance EC and NPC proliferation and induce neovascularization following stroke via SPK2, SIP, and Akt/eNOS. This project will study a novel system that can provide long-lasting improvement in brain function following stroke and serve as a target for stroke therapy.